Custom Sensors, Inc.

CCD Barcode Scanner, Barcode Reader,Converter

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How Are Barcodes Read and Decoded?

All barcode scanners use some sort of a light source and photodetector as the basis of the scanning system. In general, light is projected onto the barcode symbol. If the light strikes a black bar it is absorbed and little light is reflected. If the light strikes a white space, most of it is reflected back in the general direction of the source of the light. By having an optical system that only looks at a very small area, roughly the size of the smallest bar or space in the code, each individual bar and space can be read by the optical portion of the reader. This involves moving this small reading area over the code symbol, or if the reading area is in a fixed position, then the code is moved past it. Somehow this small reading aperture must sweep across the code symbol from first bar to last. This results in an electrical signal that represents the barcode with narrow electrical pulses representing the narrow bars or spaces and wider electrical pulses representing the wider elements of the code. It is then necessary to determine what this pattern of wide and narrow elements is to decode the barcode. This is usually accomplished with some type of microcomputer of microcontroller circuit. The decoder performs three basic functions. It times the duration of the electrical pulses and classifies them as wide or narrow bars or wide or narrow spaces. Once this is done it translates the bar and space pattern into the actual characters that make up the barcode. The last function is to transmit this barcode data to some other device that will use the data. This is usually done by transmitting the data as ASCII characters through a serial or parallel computer interface.

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